It is well known that there are certain gases which are absorbed into the surface of certain metals. These metals each have a characteristic maximum absorption level, which having once been reached through sufficient exposure to a given gas, remains unchanged unless the equipment is exposed to certain other media, for example, air or water vapor.
This characteristic of absorption can be troublesome, especially in certain delicate applications; for example, in the field of monitoring ambient air. These tests are usually carried out on automatic machines which must be calibrated by flowing a sample gas therethrough and adjustment of the machine such that the readings produced by the sample gas match the known concentrations of the sample gas constituents. In order to assure accurate calibration, the constituents of the sample gas must remain in the same concentration after passage through gas handling equipment as measured by the laboratory which produced it, so that the concentrations measured on a previously-calibrated instrument are in fact the same as those to be detected by the machine to be calibrated. Furthermore, gas handling equipment generally carries contaminants such as residual moisture or oils on surfaces thereof and such contaminants may react with and thus alter the relative concentrations of constituents of sample gases.
It is therefore necessary to insure that the gas handling equipment used to convey the sample gas from the container in which it is shipped into the machine to be calibrated does not interact with the gas and alter the relative concentration of its constituents. Clearly, the same difficulty must be dealt with in all situations where the composition of a gas is critical, whether for calibrative, chemical, anesthetic, industrial or other purposes.